The aim of the proposed research is the further elucidation of the functional organization of the vertebrate spinal cord, utilizing electrophysiological techniques. The main thrust of our research effort at present is in the identification of specific categories of spinal cord neurons and in the study of their response characteristics. The experiments currently planned will be upon the cells of origin of the spinothalamic tract in the monkey. A quantitative study of the responses of these cells to controlled mechanical and thermal stimulation will be one main effort. Another major emphasis will be upon descending pathways which control activity in spinothalamic tract neurons. In particular, the raphe-spinal tract will be investigated further, as well as the reticular formation.